Needle vibrating control mechanism for buttonhole sewing machines

ABSTRACT

A mechanism for controlling the different zigzag stitches required along the sides and at the ends of a stitched buttonhole which may be operated at high speed and accommodated readily in the severely limited space available within the sewing machine frame. A primary crank mechanism provides the reciprocatory motion required for the zigzag side stitches along each side of the buttonhole. A sleeve in which the primary crank mechanism is journaled eccentrically provides a secondary crank mechanism which may also be rotated to augment the reciprocatory motion provided by the primary crank thus to produce the barring stitches at each end of the buttonhole. The sleeve may be stopped in positions angularly spaced one half revolution apart after each barring operation so as to locate the side stitches on opposite sides of the buttonhole.

[111" 3,795,20 1 Mar. 5,1974

1 I NEEDLE VIBRATING CONTROL MECHANISM FOR BUTTONHOLE SEWING MACHINES [76] Inventor: Giinter Tiille, 752 Bruchsal 4/ Wendelinusstr. 15, Bruchsal, Germany 22 Filed: Feb. 16, 1973 21 App1.No.:333,257

[30] Foreign Application Priority Data Apr. 8, 1972 Germany 2217000 [52] US. Cl .l ll2/ 158 B [51] Int. Cl D05b 3/06 [58] Field of Search 112/65, 66, 70, 73, 158 R, 112/158 B, 158C Primary ExaminerWerner H. Schroeder Attorney, Agent, or Firm-Marshall .l. Breen; Chester A. Williams, Jr.; Robert E. Smith 1 5 7 ABSTRACT A mechanism for controlling the different zigzag stitches required along the sides and at the ends of a stitched buttonhole which may be operated at high speed and accommodated readily in the severely limited space available within the sewing machine frame. A primary crank mechanism provides the reciprocatory motion required for the zigzag side stitches along each side of the buttonhole. A sleeve in which the primary crank mechanism is journaled eccentrically provides a secondary crank mechanism which may also be rotated to augment the reciprocatory motion provided by the primary crank thus to produce the barring stitches at each end of the buttonhole. The sleeve may be stopped in positions angularly spaced one half revolution apart after each barring operation so as to locate the side stitches on opposite sides of the buttonhole.

' 7 Claims, 12 Drawing Figures PATENTED 5 74 summr PAIENIEUHAR 5:974

SHEEI 2 BF 3 BACKGROUND OF THE INVENTION Prior buttonhole sewing machines have been provided in which the different zigzag stitches required to form a buttonhole are produced. by the operation of regulating mechanisms for changing the needle jogging motion. The U.S. Pat. No. 2,056,758 of E. B. Allen et al is representative of such prior buttonhole sewing machines. These known mechanisms require extensive needle jogging control linkages extending considerable distances through the machine frame from'a number of different control devices such as cams or the like. Such extensive linkages are not conductive to high speed operation, nor are they adapted to inclusion in a sewing machine frame in which space is-limited. a crank The U.S. Pat. No. 2,983,340 May 9, 1961 of W.

Engel discloses a needle vibrating control for buttonhole sewing in which a primary'pattern cam for influencing the buttonhole side stitch zigzagging which is operated continuously is' augmented bya periodically operating auxiliary pattern ca'mto produce the wide zigzag stitches of the buttonholebars. This known construction thus requires separate spring loaded pattern cam follower mechanisms for the primary and auxiliary pattern cams and, therefore, is not only severely'limited as to the speedat which it can'be operated, but is not welladapted for'use in a croWded seWing" machine frame. I

BRIEF SUMMARY O THEINYENTION It is an object of this invention to provide a needle vibrating control mechanism for. a high speed buttonhole I machine which is compact so that it can be accommodated readily in the severely restricted spacewithin the v frameof a sewing machine adapted to be ganged with DESCRIPTION OF THE DRAWINGS.

In the accompanyingdrawings this invention is illustrated in a preferred embodiment in which:

FIG. 1 is a side elevational view ofa buttonhole sewing machine with portions broken away to illustrate this invention applied thereto,

FIG. 2 is disassembled perspective view of the clutch mechanism for providing the wide barring stitches at each end of the buttonhole with the clutch elements each positioned so as to expose the clutch faces,

FIG. 3 is a perspective view of the driving'clutch element positioned so as to expose the face opposite the clutch face,

FIG. 4 is an elevational view of that face of the driving clutch element illustrated in FIG. 3 together with the driven clutch element shown held out of engagement of the clutch faces and in a position wherein clutch engagement can begin,

FIG. 5 is an elevational view similar to that of FIG. 4 but showing the clutch mechanism parts in a position of full clutch engagement, I

FIG. 6 is a disassembled perspective view of the control lever and associated parts for influencing engagement of the clutch,

FIG. 7 is an enlarged vertical cross sectional view of that portion of the needle jogging mechanism of this invention adjacent to the needle jogging crank,

FIG. 8 is a cross sectional view taken substantially along line 88 of FIG. 7, 5

FIG. 9A is a set of three diagrammatic views depict- I ing the needle jogging crank arrangement positioned for side stitching along one side ofa buttonhole, a representation of the path of the crank pin, and a representation of the buttonhole portion produced thereby,

FIG. 9B is a set of three diagrammatic views similar to those of FIG. 9A but showing the needle jogging crank arrangement positioned for side stitching along the opposite side of a buttonhole, I

FIG. 9C is a set of two diagrammatic views depicting the path of the crank pin when the outer eccentric rotates with the crank pin, and a representation of the barring stitches of the buttonhole produced thereby, and

FIG. 10 is a perspective view of the drive linkage con- 'necting the needle jogging crank with the needle bar gate.

Referring to the drawings, the buttonhole'sewing machine in which this inventionis embodied includes a base 11 formed with spaced upstanding ears 12. Swingable on a pivot pin 13 extending between the ears 12 is a bracket arm 14 carrying a loop taker 15 which may take the form of a rotary hook or any other known lockstitch loop taker. The 'loop taker may beactuated 'bysuitable operative connections with an arm shaft 16 journaled in the bracket arm 14 and carrying a sprocket 17 on which a timing belt 18 is entrained. THe timing belt extends in mesh with a driving sprocket 19 fast on a main shaft 20 journaled in the base II. V

A needle carrying bar is journaled for endwise reciprocation in a swinging gate 31 supported on vertically spaced pintles 32 carried in the machine frame base 11. Endwise reiprocatory movement is imparted to the needle carrying bar 30 by means of a drive link 33 formed at the upper end witha boss 34 slidably embracing astud '35 secured so as to extend laterally from the needle carrying bar. At the lower extremity the drive link 33 is formed with a boss 36 which engages a crank 37 carried by the rriainshaft 20.1A slot 38, formed in the drive link boss 34 embraces a stabilizing bar 39 carried in the machine frame base to steady the drive link against lateral jogging movement of the stud 35.

A thread carrying needle (not shown) clamped in the upper extremity of the needle carryinghar 30 reciprocates upwardly through work fabrics held in a work clamp indicated generally at 40 for cooperation with the loop taker 15 in the formation of lockstitches.

Although this invention may be used with work clamps having any known configuration and arrangement, as shown in the drawings, the work clamp may comprise a work engaging upper jaw 41 supported by an arched arm 42 pivoted as at 43 relatively to a lower jaw with which a work supporting plate 44 is associated. The pivotally connected jaws which can be opened by raising the upper jaw 41 to accept work fabrics therebetween, constitute a unit which is guided for linear movement relatively to a base plate 45 which is pivoted on a pivot pin 46 extending between the ears 12 of the machine frame base 11. The base plate 45 may be swung up about the pivot pin 46 carrying the lower jaw and work supporting plate 44 of the work clamp upwardly with it to provide access to the needle bar as for threading of the needle or the like.

A roller 50 carried by the bracket arm 14 and engaging a track 51 on the upper jaw 41 of the work clamp 40 maintains-a uniform distance between the work clamp jaws and the loop taker, and when the bracket arm 14 is turned down into operative position, as shown in the drawings, the base plate 45 engages a spring loaded plunger 52 in the machine frame base which biases the work clamp against the roller 50.

The mechanism shown in the accompanying drawings for shifting the work clamp back and forth to define the length of the buttonhole is described indetail in my co-pending US. patent. application Ser. No. 333,258 filed Feb 16, 1973 to which reference may be had.

Briefly, for a general understanding of this invention, it will be sufficient to understand that the work clamp is shifted by an angle bracket-60 secured to a threaded stud shaft 61 which engages a threaded bore formed in a sprocket wheel 62 supported for turning movement on the machine frame base. Intermittent turning movement is imparted to the sprocket wheel 62 by indexing mechanism indicated generally at 63 in-the drawing which imparts step-by-step movements to the sprocket The control lever 67 is carried ona fulcrum pin 81 in the machine frame base 11, and is formed with a stop finger 82 which is integral with the control lever and carries an adjustable stop finger 83 secured to the control lever by fastening screws 84 which pass through elongated apertures 85 in the stop finger 83. The stop fingers 82 and 83 cooperate alternately with diametrically opposed radial abutment projections 86 and 87 of a stop cam 88 adjustably secured to a worm wheel 89 by screws 90 which pass through elongated arcuate slots 91 on the stop cam. Also secured as by locating pins 92 to the worm wheel 89 is a feed .reversing cam 93 having diametrically opposed cam lobes 94. The worm wheel 89 is freely journaled on a stud shaft 95 carried in the machine frame base 11. The clutch device 80 is the control center for the operation of the buttonhole machine in that it changes the direction of feed of the work clamp; it influences the production of various different types of zigzag stitches produced by the machine during the course of the stitching of a buttonhole; and it can control many other functions of the machine which are not of direct concern to the present invention such as cutting, thread severing, and stopping at the conclusion of each sewing cycle. 7

This invention relates to the control mechanism whereby lateral vibration of the needle is derived and regulated. Although not directly related to this invention, the mechanism for controlling the direction of feed of the work clamp is so closely associated with the present invention that it will be described in some detail herein to facilitate a clear understanding of the present invention.

Referring to FIGS. 7 to 10, the manner in which lateral jogging movement is imparted to the needle bar can be explained and a general explanation can be given of the manner in which the various needle jogging motions are derived at the different stages of buttonhole production.

As shown in FIG, 7, 9A and 9B, a plain rotary driver in the form of a crankpin serves to impart the lateral needle jogging motion. FIG. 10 illustrates the linkage connections between the crank pin 100 and the needle bar gate 31. This needle jogging linkage forms the subject of a co-pending US. patent application Ser. No. 333,259 filed Feb. 16, 1973 to which reference may be had for a more detailed description. For comprehension of the present invention it will be sufficient to understand that a drive link 101 at one end embraces the crank pin 100 and at the other end embraces a pivot pin 102 which may be secured in selected posi tion along a slotted lever arm 103 ofa bell crank lever 104 supported on a fulcrum pin 105 in the machine frame base. The other lever arm 1060f the bell crank lever 104 is formed by a flat leaf spring which sustains a spherical connection 107 with a connecting link 108 to the needle bar gate. The connecting link 108 like the lever arm 106 is formed by a flat leaf spring, and the flexibility of these leaf springs each transversely of the directions in which they transmit forces to the needle bar gate reconcile without binding the slight differences between the arcuate and planar paths of motionof the various parts. 1

FIGS. 9A, 9B and 9C illustrate diagrammatically in a general way the derivation of the various needle jogging motions required in the production of a stitched buttonhole. The crank 100 is carried directly on a countershaft 110 which is journaled so as to rotate about an axis AA in a bearing lll supported in a sleeve 112. The sleeve 112 constitutes a second shaft journaled on a fixed axis BB in the machineframe as will be described in detail below. The bearing lllis supported eccentrically of the axis BB in the sleeve. An additional eccentric 113 is interposed between the bearing 111 and the sleeve I12 but this, as will be described in detail hereinbelow, simply provides for adjustment of the effective eccentricity of the bearing 11] relatively to the axis B--B of the sleeve 112.

The countershaft 110 rotates constantly during operation of the machine and this rotation generates the small diameter paths of motion 114 of the crank pin 100 as illustrated in FIGS. 9A and 9B. The small diameter path of motion of the crank pin 100 produces the narrow zigzag side stitches of the buttonhole. In these FIGS 9A and 9B, the sleeve 112 is constrained in a position sustaining the countershaft in an extreme upper position so that the narrow zigzag stitches 115 along the right-hand side of the buttonhole will be produced. In FIG. 9B; the sleeve 112 is constrained in a position onehalf revolution beyondthat of FIG. 9A and as shown, the narrow zigzag stitches 116 along the lefthand side of the buttonhole will be produced.

The space 117 between the side stitches 115 and 116 provides cutting space for the buttonhole. A cutting space exists because the eccentricity of the bearing 111 exceeds the eccentricity of the "rotatable'driver crank pin and this may be regulated by selective adjustment of the additional eccentric 113 as will be ,explained hereinbelow. e

When the sleeve 112 is rotated in synchronismwit h the countershaft with the crank pin 100 in either the upper extreme position shown in FIG. 9A or in the lower extreme position shown in FIG. 9B, the crank pin will generate the large diameter path of motion 119 as shown in FIG. 9C during which the wide zigzag stitches 118 will be formed providing the barring stitches at the ends of the buttonhole.

The adjusting eccentric 113 is formed with a radial flange 120 in which arcuate slots 121 are formed. The slots accommodate clamp screws 122 threaded each into a radial lug 123 protruding from the sleeve 112. A cover plate 124 exteriorly of the eccentric flange 120 provides a surface which may be provided with indicia (not shown) cooperating with marks on the eccentric flange 120 to show the position of adjustment, for in-' stance, to indicate the cutting space which will be provided in each possible position of adjustment. Referring to FIGS. 1 to 5, the mechanism for influencing constant rotation of the countershaft 110 and periodic rotation of the sleeve 112 with constraint,

thereof alternately in positions one-half I revolution apart will now be described. v

A bushing fixed in a web 131 of the machine frame base 11 accommodatesan anti-friction bearing 132 in fixed position therein between a shoulder 133 and a split locking ring 134. The bearing 132 is Similarly locked in place between a shoulder 135 anda locking clip 136 on a shank port ion 137 of the sleeve 112. The sleeve 112 is'thus carried for rotation but constrained against'endwise shift in the machine framel Also interposed between the bushing .130 and the sleeve shank 137 is a one-way roller clutch 138 and a anti-friction needle bearing 139.

The free extremity of the sleeve shank 137, as best shown in FIG. 2, is formed diametrically with a slot 140 which slidably accommodates a diametrically slabbed key 141 formed on a hollow driven clutch hub member 142 of which the exterior 143 is formed with a step 144. Force fit or otherwise rigidly secured to the exterior 143 .of the driven clutch hub member 143 against the step 144 is a metal corel45 on which is molded a synthetic plastic driven clutch shoe 146 which includes a tapered non-circular clutch face 147. Projecting from the metal core is a radial arm 148 to which a block 149 is secured. g

The core 145 is formed with a counterbore 150 which accommodates one end ofa compression spring At the extremity of the clutch hub 142 opposite the worm 156, the hub is formed with securing tangs 158 which are clinched into locking engagement with mating recesses 159 in a pilot nose element 160 formed with an inclined slabbed portion 161. Internally in the driven clutch hub member 142 adjacent to the pilot nose element 160 as shown in FIG. 1, a needle bearing 162 is provided between the clutch hub member and the countershaft 110. The countershaft 110 at the extremity opposite the crank pin 100 is threaded as at to accommodate adriving clutch hub member 171. A splitthreaded portion 172 of the hub member 171 is provided with a set screw 173.by which the split portion may be deformed to secure the hubmember fast in selected angular position on the countershaft 110. The driving clutch hub member 171 is formed with an exterior step 174 against which an anti-friction bearing 175 is seated. The hub member 'is exteriorly threaded as at 176 to accommodate a threaded belt pulley 177 which locks the bearing 175 in place against the step 174. The anti-friction bearing 175 is supported in a hollowbushing 178. seated in a web 179 in the machine frame base 11. l

Secured by screws 180 to the pulley 177 is a metal core 181 on which a synthetic plastic driving clutch shoe 182 is molded. The clutch Shoe 182 includes a mpered non-circular clutch face 183 which is complemental to the driven clutch face 147 on the driven clutch shoe 146. The metal core 181 also supports a metalic outer ring 184 formed with a lateral driving lug 185 adapted to cooperate'with the block 149 on the driven clutch core'during disengagement of the clutch 15.1 of which the opposite end abuts a stop washer 152 formed with a'slot "153 snugly accommodating the slabbedkey 141. The washer, therefore, abuts the free extremity ofthe sleeve shank 137 so that the spring 151 will urge the driven clutch shoe 146 toward the right as viewed in FIG. 1. e

The slabbed key 141 of the clutch hub is formed with notches 154 accommodating inwardly extending lugs as will be described below.

A timing belt 186 operably connects the .belt pulley 177 on the countershaft with a driving pulley 187 on the main shaft 20. Thecountershaft 110,'therefore, will be rotated continuously during the operation of the sewing machine .main shaft.- The driving clutch shoe 182 similarly will be rotated continuously. Because of the meshing arrangement of the worm 156. with the worm wheel 89, the sleeve 112 will be-rotated-periodically in synchronism with the countershaft 110 and will be alternately stopped in diametrically opposite positions in a manner which will now be described.

When either the fixed stop finger 82 or the adjustable stop finger 83 on the control lever 67 engages one of the radial projections 86 or 87 on the stop cam 88, turning of the worm wheel 89 will be stopped and the worm 156, as it continues to be driven by the engaged clutch shoes 146, 182, will move axially to the left as viewed in FIG. 1 continuing to turn the sleeve 112 but drawing the clutch faces 146, 182 apart into the declutched position as shown in FIG. 1..

)When the clutch faces are fully engaged, as shown in FIG. 5, the block 149 and driving lug-185 will be separated and the non-circular clutch faces 147, 183 fitting one within the other willtransmit-all of the motion to the sleeve 112. As disengagementof the clutch begins, the block 149 will immediately shift into engagement with the driving lug 185 to maintain driving relation between the clutch path until they are shifted completely apart as shown in FIG. 1.

The one-way clutch 138 will prevent retrograde movement of the worm 156 and the restrained stop cam 88 will prevent retrograde movement of the worm wheel 89 so that, in turn, the worm 156 will be preventedfrom sliding axially along the sleeve shank and ing 111. Each of the two alternate stopped positions of the sleeve 112 moreover, can be adjusted indepenworm wheel 89 by virtue of the screws 90 effects adjustment of one stopped position; and positioning of the adjustable stop finger 83 by the screws 84 effects adjustment of the other stopped position.

When the control lever 67 is swung to disengage and free the stop cam 88, the worm wheel 89 is released and the worm 156 becomes free to shift axially toward the right as viewed in FIG. 1 under the action of the spring l51 toward engaged position of the clutch faces 147, 183. Clutch engagement is purposely delayed, however, in order to provide gradual clutch engagement over the largest possible angular interval. Because of this gradual engagement of the clutch faces, the clutch becomes operable at far higher speeds than would be possible if sudden engagement were to be attempted. The gradual engagement minimizes rebound. Delayed clutch engagement is provided by means of a blocking lever 190 which is arranged in a cutout 191' of the metal core 181 of the driving clutch shoe and urged by a spring 192 into a position traversing a portion of a bore 193 in the core 181 into which the nose element 160 is accommodated. The blocking lever 190 may be formed with a rounded fulcrum projection 194 constrained in a mating seat 195 in the core 181 pivotally to support the lever thereon. Until the inclined slabbed portion 161 of the nose element 160 moves into registry with the blocking lever 190, the driven clutch shoe 146 will be prevented from moving toward the driving clutch shoe 182. As shown in FIG. 4, this position of registry occurs when the block 149 first clears the lug 185 thus allowing the greatest angular increment for gradual engagement of the clutch faces 147, 183.

Having set forth the nature of this invention, what is claimed herein is:

1. In a buttonhole sewing machine in which the needle is carried in a gate laterally shiftable in the sewing machine frame and connected by a linkage to a rotatable drive, a mechanism for imparting to the needle lateral jogging movements of a narrow width along each side of the buttonhole and of a wide width at' the ends of the buttonhole,'comprising a first shaft having an axis of rotation and carrying said rotatable driver eccentrically of said axis of rotation thereon, a second tive between said second shaft and said sewing mashaft journaled on a fixed axis in said sewing machine frame, a bearing for said first shaft supported eccentrically of said fixed axis on said second shaft, the eccentricity of said bearing exceeding the eccentricity of said rotatable driver, continuously operative drive mechathe ends of the buttonhole as a result of the sum of the eccentrieities of said rotatable driver and of said bear- 2. A needle jogging mechanism as set forth in claim 1 in which means is provided for adjusting the difference by which the bearing exceeds the eccentricity of the rotatable driver so that the buttonhole cutting space between the buttonhole side stitches may be regulated.

3. A needle jogging mechanism as set forth in claim 2 in which said adjusting means comprises an additional eccentric interposed between said second shaft and said bearing and a clamping device for securing said additional eccentric in selected angular position relatively to said second shaft.

4. Aneedle jogging mechanism as set forth in claim 1 in which the periodically operative drive mechanism for the second shaft comprises a driving clutch element fixed on said continuously driven first shaft, a driven clutch element rotatably interlocked with said second shaft, mechanism for axially shifting said driven clutch element into and out of engagement with said driving clutch element, and'means for restraining said driven clutch element in diametrically opposite positions of rotation on alternate shifts out of engagement with said driving' clutch element.

5. A needle jogging mechanism as set forth in claim 4 in which said means for restraining said driven clutch element in diametrically opposite positions of rotation comprises a worm secured for turning-and axial shifting with said driven clutch element, a worm wheel journaled in said sewing machine and meshing with said worm,- abutments secured to said worm wheel and cooperable with stop fingers on said sewing machine frame for selectively arresting rotation of said worm wheel, and retrograde clutch means continuously effecchine frame.

6. A needle jogging mechanism as set forth in claim 5 in which tripping mechanism is provided responsive to the operation of the buttonhole sewing machine for releasing said stop fingers to re-establish the periodically operative drive for said second shaft at each end of a buttonhole.

7. A needle jogging mechanism as set forth in claim 4 in which said driving and said driven clutch elements are formed with non-circular complemental clutch faces which in fully engaged condition establish a predetermined angular relationship between said driving and driven clutch elements, and in which said driving and driven clutch elements include blocking means effective when the clutch elements are disengaged to permit axial movement of the clutch faces toward full engagement to begin in only that oneangular relationship between said driving and driven clutch elements which is substantially one full revolution in advance of said predetermined angular relationship which is established in fully engaged conditionof said clutch elements. 

1. In a buttonhole sewing machine in which the needle is carried in a gate laterally shiftable in the sewing machine frame and connected by a linkage to a rotatable drive, a mechanism for imparting to the needle lateral jogging movements of a narrow width along each side of the buttonhole and of a wide width at the ends of thE buttonhole, comprising a first shaft having an axis of rotation and carrying said rotatable driver eccentrically of said axis of rotation thereon, a second shaft journaled on a fixed axis in said sewing machine frame, a bearing for said first shaft supported eccentrically of said fixed axis on said second shaft, the eccentricity of said bearing exceeding the eccentricity of said rotatable driver, continuously operative drive mechanism for rotating said first shaft during operation of said sewing machine to generate lateral jogging movements of a narrow width along each side of the buttonhole as a result of the eccentricity of said rotatable driver, and periodically operative drive mechanism for rotating said second shaft in synchronism with said first shaft to generate lateral jogging movements of a wide width at the ends of the buttonhole as a result of the sum of the eccentricities of said rotatable driver and of said bearing.
 2. A needle jogging mechanism as set forth in claim 1 in which means is provided for adjusting the difference by which the bearing exceeds the eccentricity of the rotatable driver so that the buttonhole cutting space between the buttonhole side stitches may be regulated.
 3. A needle jogging mechanism as set forth in claim 2 in which said adjusting means comprises an additional eccentric interposed between said second shaft and said bearing and a clamping device for securing said additional eccentric in selected angular position relatively to said second shaft.
 4. A needle jogging mechanism as set forth in claim 1 in which the periodically operative drive mechanism for the second shaft comprises a driving clutch element fixed on said continuously driven first shaft, a driven clutch element rotatably interlocked with said second shaft, mechanism for axially shifting said driven clutch element into and out of engagement with said driving clutch element, and means for restraining said driven clutch element in diametrically opposite positions of rotation on alternate shifts out of engagement with said driving clutch element.
 5. A needle jogging mechanism as set forth in claim 4 in which said means for restraining said driven clutch element in diametrically opposite positions of rotation comprises a worm secured for turning and axial shifting with said driven clutch element, a worm wheel journaled in said sewing machine and meshing with said worm, abutments secured to said worm wheel and cooperable with stop fingers on said sewing machine frame for selectively arresting rotation of said worm wheel, and retrograde clutch means continuously effective between said second shaft and said sewing machine frame.
 6. A needle jogging mechanism as set forth in claim 5 in which tripping mechanism is provided responsive to the operation of the buttonhole sewing machine for releasing said stop fingers to re-establish the periodically operative drive for said second shaft at each end of a buttonhole.
 7. A needle jogging mechanism as set forth in claim 4 in which said driving and said driven clutch elements are formed with non-circular complemental clutch faces which in fully engaged condition establish a predetermined angular relationship between said driving and driven clutch elements, and in which said driving and driven clutch elements include blocking means effective when the clutch elements are disengaged to permit axial movement of the clutch faces toward full engagement to begin in only that one angular relationship between said driving and driven clutch elements which is substantially one full revolution in advance of said predetermined angular relationship which is established in fully engaged condition of said clutch elements. 